Is it generally reliable asking Amazon support what capacity you need for a particular use case, so you're not buying more than needed? e.g. a service that might be used once per day for a minute, and another day it might get used a dozen times for maybe an hour, and only during fixed business hours. And there are general purpose, compute optimized, storage optimized, etc. But what if the service is more network latency sensitive than either storage or compute sensitive?

Or are there 3rd party estimators that do a better job of telling you what kind of instance to get? Or just pick a general purpose instance, run it for a week, and then tweak it?